Hollow, blow molded, thermoplastic articles enjoy widespread commercial acceptance because of ease of fabrication and reduced labor costs. Abundant applications for blow molded, thermoplastic articles are apparent in the medical field alone. Form, fill, and seal blow molded containers, designed for sterile and aseptic packaging of parenteral solutions and the like, are well known.
In certain applications, however, additional operations need to be performed on blow molded containers to decrease their water vapor permeability, decrease their permeability to gasses (especially oxygen), or provide a sterile surface on at least a portion of the outside of the container as may be desirable, particularly in the medical field. Additional layers of thermoplastic or adhesive material may be applied to blow molded containers in subsequent operations, after the article has been blown, in efforts to decrease permeability or provide a sterile surface. Subsequent operations, though, tend to be time consuming and labor intensive, thus increasing the cost of the completed article. Further still, when sterility is a factor, it is difficult to maintain acceptable control.
Heretofore, thermoplastic containers have had additional layers applied by methods such as dip coating, spray coating, shrink fit coating, or injection overmolding. See, for example, U.S. Pat. No. 3,457,337, Method for Producing Coated Containers, to Turner. Where gas permeability or water vapor permeability is important, outer layers of plastic material may be applied. Where medical uses are contemplated, the exterior of blow molded, thermoplastic containers can be sterilized by overcoating of the outer surface under sterile conditions or before terminal sterilization.
Plastic containers are often blow molded from a continuously extruded tube. Methods of coextrusion exist which comprise simultaneously extruding coaxial tubular members and then blow molding those members. Layered plastic containers are produced thereby, specifically to decrease gas or water vapor permeability of the container. See, for example, U.S. Pat. No. 4,079,850, Multi-Layer Blow Molded Container and Process for Preparation Thereof, to Suzuki, et al. and U.S. Pat. No. 3,457,337, Method for Producing Coated Containers, to Turner. Typically, though, the container layers are not easily separable or peelable because the thermoplastic materials used have been compatible, that is, they adhere at their interface.
By this invention layered, blow molded thermoplastic containers are produced by simultaneously feeding two thermoplastic materials, using existing injection or extrusion technology, into a blow molding die, extruding the simultaneously fed thermoplastic materials to form a layered parison, and then blow molding the parison.
As an additional feature, blow molded articles are provided which have the advantages of layered sealing systems without the need to provide subsequent, separate operations.
Another additional feature of the present invention is found in the flexibility afforded in locating layered sections. This invention provides a novel method of simultaneously feeding incompatible thermoplastic materials into a blow molding die to produce an optionally intermittently layered parison which is blow molded into an intermittently layered article.
Still another advantage of the present invention lies in the ability to produce a blow molded thermoplastic article with a peelable thermoplastic layer thereover, which is simultaneously blow molded with the article, and which maintains a sterile interface until removed.
Further features of the invention include providing containers with reduced gas permeability or water vapor permeability by blow molding layered, thermoplastic containers.